1. Field of the Invention
The present invention relates to an apparatus for descrambling a data retrieved from an optical storage medium and a method therefor; more specifically, relates to an apparatus and method for descrambling a data retrieved from an optical storage medium by activating an linear feedback shift register (LFSR) according to address information that is stored in a memory.
2. Descriptions of the Related Art
To retrieve a data that is recorded on an optical storage medium, an optical access system is required. As shown in FIG. 1, an optical access system 1 of the prior art comprises a servo interface 101, a decoder 103, a memory 105, a firmware 107, and an interface 109. The servo interface 101 receives a data 102 that is recorded on an optical storage medium, such as an optical disc, and transmits the data 102 to the decoder 103. The decoder 103 generates a decoded data 104 by performing, for example, error correction and error detection code (EDC) calculation on the data 102. The decoded data 104 is transmitted to the memory 105 to be temporarily stored. The interface 109 comprises a linear feedback shift register (LFSR) for descrambling the decoded data 104 to generate a digital data 106 which is recognizable for a host to be proceeded. The firmware 107 is configured to generate an initial value 108 to initialize the LFSR before the interface 109 descrambles the decoded data 104.
For BDs (blu-ray discs), recorded data are arranged in clusters each of which comprises 32 data frames and protected by 2 kinds of error correction mechanism, long distance code (LDC) and burst indicator subcode (BIS). The LDC comprises (248, 216, 33) Reed-Solomon codewords, and is used to correct random errors and burst errors. The BIS comprises (62, 30, 33) Reed-Solomon codewords, and is used to indicate long burst errors. Each data frame comprises 2052-byte data and a 4-byte EDC. Both of the 2052-byte data and the EDC are descrambled by the LFSR. To initialize the LFSR, some shift registers of the LFSR are required to be preset with the initial value 108 derived from physical sector numbers associated with data frames. Besides, the initial value 108 should be used for all 32 data frames in the same cluster.
For HDDVDs, one data frame comprises 2048-byte data and a 4-byte EDC. Both of the 2048-byte data and the EDC are descrambled by the LFSR. Similarly, some shift registers of the LFSR are required to be preset with the initial value 108 when the LFSR is initialized. The same initial value 108 is used for 16 consecutive data frames.
The firmware 107 is required to be set before data descrambling and decoding begin. Once the data decoding is interrupted by, for example, reading a replacement for a defect from an optical storage medium, the firmware 107 must re-count to re-initialize the LFSR. This seriously influences the processing speed. Accordingly, a solution to avoid re-initializing the LFSR is desired in the industrial field.